Global soil organic carbon changes with reforestation/afforestation

Soil organic carbon (SOC) changes resulting from forestation (including afforestation and reforestation) play a crucial role in evaluating the forest-pathway contribution to global climate change mitigation within the framework of nature-based climate solutions. However, forestation may fail to increase SOC and even lead to SOC decline over certain time periods, potentially offsetting the climate mitigation benefits achieved through biomass carbon sequestration. To address this, we review global studies on forestation, encompassing both plantations and natural regeneration, and analyze the factors driving SOC changes after afforestation and reforestation. Our analysis reveals that higher initial SOC tends to cause regional soil carbon loss, with topography, climate, soil condition, and land use history together determining overall SOC changes after forestation. Furthermore, we utilize random forest models to predict future SOC dynamics following forestation, with significant variability observed across climate zones in first 30 years, and the contribution of SOC to total carbon sequestration appears lower than previously estimated. These findings highlight the need for greater consideration of local conditions when designing forestation strategies to optimize ecosystem carbon sequestration, and to enhance soil’s role in achieving sustainable climate change mitigation goals.